Election Countdown: Trump jumps into Ohio special election fight | What to watch in Tennessee primaries | Koch network freezes out Republicans who crossed them | Dead heat in Texas, Nevada Senate races | How celebs are getting into the midterms

This is Election Countdown, The Hill's weekly newsletter from Lisa Hagen (@LA_Hagen) and Max Greenwood (@KMaxGreenwood) that brings you the biggest stories on the campaign trail. We'd love to hear from you, so feel free to reach out to Lisa at LHagen@thehill.com and Max at MGreenwood@thehill.com. with any questions, comments, criticisms or food recommendations (mostly the latter, please).

We're 97 days until the 2018 midterm elections and 825 days until the 2020 elections.

PresidentTrump has been selective about candidate endorsements -- factoring in where he can have the most impact, while avoiding being tied to an embarrassing loss. That dynamics is at work again ahead of Tennessee's primaries on Thursday.

The gubernatorial primary to replace term-limited Republican Gov. Bill Haslam is the race to watch and one in which the president is notably staying neutral.

And in the race for Diane Black's seat, five Republicans are running including former state Agriculture Commissioner John Rose, who's deeply connected in the district and the leading fundraiser. The president won the 6th district by nearly 50 points, and candidates are touting their support for Trump.

A day before the primary, Blackburn launched her first TV ad of the campaign that focuses on her "strong Tennessee values." Bredesen has also been on the air.

Democrats' Senate Majority PAC has indicated that it believes it's worth investing in the Tennessee race and has made reservations for August and fall TV ads.

Special election primer

We're less than a week out from Ohio's special election and things are heating up quickly as Republicans scramble to hold on to a reliably red seat, where Trump won by 11 points in 2016.

Republican Troy Balderson appeared to have the edge for months over Democrat Danny O'Connor, but a new Monmouth University poll out Wednesday -- the first public poll since June -- has the race as a toss-up.

The poll comes on the heels of news that Trump will hold a rally Saturday night in the Columbus suburbs to help Balderson. Trump's visit could give him a boost among the base, whose voters are critical in low-turnout races like special elections.

A lot can happen over the next six days and the race is clearly still wide open, but Democrats are likely feeling pretty good about their current position. If they pull off an upset victory, it'll give them the narrative they've been looking for: that Democrats can compete in GOP-leaning suburban districts that will be key to taking back the House.

Florida's Senate race is also pretty close:A new Mason-Dixon poll shows Gov. RickScott (R) leading Sen. BillNelson (D) by 3 points, 47 to 44 percent. The poll is within the margin of error, but it's good news for Scott, who previously trailed Nelson.

In a new poll from OH Predictive Insights, McSally is the front-runner in the Aug. 28 GOP primary, leading former state Sen. Kelli Ward by 8 points. But McSally still trails Rep. Kyrsten Sinema (D-Ariz.) by 4 points in a hypothetical general election match-up.

Three new NBC/Marist polls out last week bode poorly for Republicans in three potential battleground states. The survey shows Trump's approval dwindling in Wisconsin, Michigan and Minnesota.

In Wisconsin, one of the state's Trump flipped in 2016, 61 percent of registered voters said they want to "give a new person a chance" in the governor's mansion. That's a bad sign for Gov. Scott Walker (R), who's seeking a third term in office. Sen. TammyBaldwin (D) is also leading her two possible Republican challengers by at least 15 points, the NBC/Marist poll found.

What we're watching for

Primary season is back, starting with the Tennessee primaries tomorrow. The next ones will be held Aug. 7 in Kansas, Michigan, Missouri and Washington. That is also the date for Ohio's special election.

The Cramer remarks were made to Reuters in March also called defense spending a "very high priority" and his criticism seemed to be directed at GOP leaders' handling of a massive spending bill.

Cramer's response features a group of military veterans sitting around a table. "I like Heidi. Who doesn't like Heidi? But I don't like the way she votes in Washington," one woman, identified as a retired lieutenant colonel, says, about Sen. Heidi Heitkamp (D-N.D.).

Rep. Dana Rohrabacher (R-Calif.), who is in the midst of a competitive race with Democrat Harley Rouda, this week defended the 2016 meeting between Trump campaign officials and a Russian lawyer promising dirt on Clinton. Rohrabacher told Mother Jones' David Corn that "there's not a person in this town who would not take a meeting to get material like that."

A handful of Hollywood celebrities are getting ready to back Democratic candidates ahead of the midterms, The Hill's Judy Kurtz reports. Experts say that liberal celebs hoping to stymie Trump are likely to become more active over the next three months. GOP critics, however, were quick to point out what happened when celebrities went all in on Hillary Clinton's campaign.

Forrmer President Obama on Wednesday also unveiled a list of 81 endorsements of Democratic candidates in races across the country. But Obama also kept his distance from some high-profile races. Notably not on the list were Alexandria Ocasio-Cortez and Rep. Beto O'Rourke (D-Texas), who is running for Senate.